Semiconductor manufacturers must continually improve the power and performance of semiconductor devices while keeping the device size to a minimum. In an effort to maintain a small device size, most semiconductor manufacturers reduce individual components of the device to minimal dimensions. Further, manufacturers are vertically integrating more and more of these components, as opposed to using only horizontal integration, to reduce the device area consumed by the components. Vertical integration is typically achieved by using several conductive layers in the device and interconnecting these layers using, for example, interlevel contacts.
As individual component dimensions become smaller, it becomes more difficult to interconnect the various conductive layers. Attributing to the difficulty is the inability to resolve very small dimensions without having to invest in the best optical lithography equipment available. As in any industry, it is advantageous from a cost point of view to get the most performance out of currently owned equipment rather than having to continually and frequently upgrade to new equipment. A problem with using existing lithography equipment in semiconductor manufacturing is difficultly in properly aligning a contact and forming a contact opening in a very small region. A popular approach in the industry to form contacts in small regions is to use self-aligned contact structures. Self-aligned contact structures permit contacts to be made in spaces which are smaller than the space actually printed by optical lithography techniques. For example, a 0.5 .mu.m contact can be formed in a device even though the resolution of a particular piece of optical lithography equipment is 0.8 .mu.m. Furthermore, a self-aligned contact has more lenient alignment tolerances, meaning that a misaligned printed contact opening may still be sufficient to permit reliable contact. One disadvantage is that most self-aligned contact structures rely on underlying topography, such as underlying conductive lines, to define the contact area. The distance between adjacent conductive lines and the thickness of insulating materials overlying these lines govern the dimensions of self-aligned contacts. Because of this dependency, many self-aligned contact structures are termed "pitch dependent," where pitch refers to the distance from the center of one conductive line to another. Furthermore, many existing self-aligned contact processes cannot be used to form contacts in isolated regions of a semiconductor device in which little or no underlying topography exists. Therefore, forming contacts in isolated regions usually requires a non-self-aligned contact formation which typically cannot occur at the same time a self-aligned contact is formed. Devices employing both self-aligned and non-self-aligned contacts at approximately the same level in a device must undergo a sequence of contact formations which undesirably increases fabrication time and fabrication cost.
Therefore, a need exists for an improved method for forming a contact in a semiconductor device, and more specifically for a method which forms pitch-independent contacts and has the ability to form both self-aligned and non-self-aligned contacts simultaneously.